The present invention relates to a color registration error detecting method for detecting an error of a color image forming position (which will be hereinafter referred to as a color image registration) for use in a color image forming device for transferring multiple images of different colors onto a recording member or an intermediate transfer member to obtain a color image. More particularly, the invention relates to a color registration error detecting method for determining an interval and the number of times of computation of pattern positions as a basic for detecting color image registration error.
In recent years, colored documents have increasingly been processed in offices and the like, and accordingly image forming devices handling such color documents, such as copying machines, printers, facsimiles, etc., have also increasingly need to have the capacity to accommodate colored documents. Further, at present, a need exists for such color equipment to be improved in image quality and operation speed consistently with high quality and high speed business processes in offices or the like.
As color equipment capable of meeting this requirement, there has already been proposed a so-called tandem type color image forming device having a plurality of color image forming units for different colors of black (K), yellow (Y), magenta (M), and cyan (C) to transfer multiple images having the different colors formed by the image forming units onto a recording member of an intermediate transfer member thereby forming a color image.
Such a tandem type color image forming device is designed to form a color image by using a plurality of image forming units. Accordingly, the device operation speed is very high, but the images of the different colors are apt to slip, that is, an error of color registration is apt to occur, causing a significant defect which makes it difficult to obtain high quality for the color image. The registration defect is due to the fact that a change in internal temperature of the image forming device, or application of an external force to the image forming device, causes a fine change in position of each image forming unit or parts in each image forming unit. The change in internal temperature of the image forming device and the application of an external force to the image forming device are unavoidable. For example, a routine operation such as removal of jamming, parts replacement in maintenance, and movement of the image forming device causes the application of an external force to the image forming device.
To solve this problem, there has been proposed in Japanese Patent Laid-open Publication No. 1-183676 a color registration error detecting method for realizing high quality of a color image by correcting a color image registration. This method includes the steps of generating a predetermined registration error measurement pattern from each image forming unit, reading this pattern by using pattern detecting means, calculating a color registration error from a detection signal from the pattern detecting means, and correcting each image forming unit so as to eliminate the color registration error, thus realizing high quality for the color image.
However, this prior art method has the following problem. In reading the predetermined registration measurement patterns, the pattern detecting means also reads vibrational components in addition to the original color registration error be measured. The vibrational components include:
i) A vibrational component resulting from the registration error measurement patterns themselves, that is, a vibrational component due to the fact that the registration error measurement patterns are not strictly equally spaced from each other.
ii) A fluctuation in position or speed of a paper feed mechanism, a recording paper, or an intermediate transfer member.
iii) A vibration of the pattern detecting means itself.
Accordingly, a great loss occurs in the accuracy of detection of the color registration error, and it is therefore difficult to obtain a high-quality image in spite of the correction of each image forming unit. Further, the higher an image forming speed, the larger the above vibrational components, causing further loss of detection accuracy of the color registration error. Thus, high quality and high image speed forming cannot be realized simultaneously. Thus, the described vibrational components make it difficult to develop a high-quality, high-speed color image forming device.